Setting up a Barometer.

A Barometer should be adjusted according to the altitude of their location which is a factor of variation. This can be done, for instance, by comparison with the town or local barometer.
Adjusting screw on the back of the barometer is very small sometimes just visible through a plastic casing: Using a very small screwdriver and turning the adjusting screw in the right direction, until the black pointer reaches the division corresponding to the one on the standard barometer. (Be careful that there should be no pressure or weight applied to the screwdriver whilst making the adjustment as it will affect the barometer reading) If for example the local pressure is 1018 millibars when setting your barometer advance the needle to just below that position, re-hang your barometer to its desired place and then lightly tap the face, it should move up or down from the position just set.
You may have to perform these actions a couple of times until your barometer shows the correct setting. Once accomplished and set for your location it should not require resetting for some years providing it is not moved around, as they are very sensitive instruments.
On a weather forecast the barometric pressures are often displayed in Millibars you should adjust it as close as possible for your location. A regular tap on the barometer is to allow the vacuum cylinder and indicator mechanism to perform freely, giving a more constant display of air pressure. Mounted on the barometer's glass is an indication needle. This needle is used to record barometric pressure. Simply line up the needle with the barometer needle inside the case. You will see any changes over time in the barometric pressure, by noting the difference between the inside and outside needle.